2-(P-Aminophenyl)-6-Methylbenzothiazole
|
HS Code |
216281 |
| Chemical Formula | C14H12N2S |
| Molecular Weight | 240.32 g/mol |
| Appearance | Solid (usually) |
| Color | Typically off - white to light yellow |
| Melting Point | 158 - 162 °C (approximate) |
| Solubility In Water | Poorly soluble |
| Solubility In Organic Solvents | Soluble in some organic solvents like ethanol, chloroform |
| Odor | Weak, characteristic odor |
| Stability | Stable under normal conditions if protected from light and moisture |
| Purity | Can be found in various purity levels, often >95% in commercial products |
As an accredited 2-(P-Aminophenyl)-6-Methylbenzothiazole factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 100g of 2-(P - Aminophenyl)-6 - Methylbenzothiazole packaged in a sealed bottle. |
| Shipping | 2-(P - Aminophenyl)-6 - Methylbenzothiazole is shipped in sealed, corrosion - resistant containers. Special handling procedures are followed due to its chemical nature. Shipment is via approved carriers, ensuring compliance with safety regulations. |
| Storage | Store 2-(p -Aminophenyl)-6 -Methylbenzothiazole in a cool, dry place, away from direct sunlight. Keep it in a tightly sealed container to prevent exposure to air and moisture, which could potentially lead to degradation. Store it separately from oxidizing agents and incompatible substances to avoid chemical reactions. |
During the manufacture of wet-end fluorescent whitening agents (FWAs) for fine paper and lightweight coated grades, 2-(p-aminophenyl)-6-methylbenzothiazole is introduced as the nucleophilic aryl-amine terminator in a two-stage cyanuric chloride condensation sequence. The compound is first suspended in ice‑water slurry at 0–5°C and reacted with an equimolar charge of 2,4,6‑trichloro‑1,3,5‑triazine while maintaining pH 3.5–4.0 through controlled addition of 20% sodium carbonate solution. This primary condensation is monitored by free amine disappearance via diazotization titration; residual aromatic amine must be kept below 0.3% of theoretical to prevent premature triazine hydrolysis that otherwise generates turbidity in the final FWA liquor. The monochloro intermediate is then transferred into a buffered aqueous‑methanol medium at 40–45°C, where it is coupled with 4,4′‑diaminostilbene‑2,2′‑disulfonic acid (DSD acid) at a stoichiometric ratio of 2.02–2.05:1. pH is maintained at 7.2–7.8 by automated sodium hydroxide dosing; excursions beyond pH 8.0 cleave the triazinyl‑chlorine bond and yield inactive hydroxy‑triazinyl byproducts that depress fluorescence quantum yield below 0.60. The resulting bis‑triazinylaminostilbene derivative is isolated as a sodium salt by spray‑drying at inlet temperature 185±5°C and outlet temperature 82±3°C to a residual moisture content of ≤5.0% w/w. Pre‑drying is mandatory when ambient relative humidity exceeds 60%, because the hygroscopic paste absorbs water that later triggers lump formation during extended warehousing. Post‑synthesis, the raw material is never blended with free primary alkylamines, which undergo transamination at the triazine ring even at 25°C, producing asymmetric dimers with a bathochromic shift that renders the FWA ineffective for cellulosic whites. The table below summarises the process window established on a 500‑L glass‑lined reactor equipped with a high‑shear rotor‑stator homogeniser (IKA Ultra‑Turrax UTL 1000, 3,000 rpm) and an in‑line pH probe (Mettler Toledo InPro 3250i).
How Does the Aminophenyl Substituent Modulate Scorch Safety in Sulfenamide Vulcanization Accelerators?A significant portion of 2-(p-aminophenyl)-6-methylbenzothiazole produced globally is converted into an intermediate for delayed‑action sulfenamide accelerators designed for low‑PAH and low‑nitrosamine tyre tread compounds. The primary amine is oxidatively condensed with tert‑butylamine or cyclohexylamine in the presence of sodium hypochlorite at −2 to 2°C in a water‑isopropanol mixture. The resulting sulfenamide, N‑(tert‑butyl)-2-[4-(6-methylbenzothiazol-2-yl)phenyl]sulfenamide, separates as a pale‑yellow crystalline solid with a melting point of 118–122°C and a purity exceeding 98% by HPLC (UV detection 280 nm). In a natural rubber compound based on SMR 20, the accelerator is evaluated at 0.7, 1.0, and 1.5 phr alongside 2.5 phr sulfur and 5.0 phr zinc oxide in a Brabender Farograph E at 50°C and 30 rpm. Cure curves collected on a MonTech MDR 2000 according to ASTM D5289‑19a reveal a scorch time (ts2) elongation from 3.2 min to 13.7 min at 140°C when the accelerator concentration moves from 0.7 to 1.5 phr, while t90 extends from 8.4 to 28.9 min. This extremely wide processing window permits multi‑cavity injection moulding of complex engine mount profiles without premature crosslinking in the runner system. The addition of 0.3 phr of para‑phenylenediamine antidegradant (6PPD) further postpones ts2 by 1.5–2.0 min due to radical scavenging, but the combination causes a plateau torque reduction of 6–8% in the vulcanizate, an effect attributed to accelerator fragmentation induced by amine‑radical cross‑reactions.The grade is intentionally produced with a maximum free amine content of 0.15% because residual 2-(p-aminophenyl)-6-methylbenzothiazole acts as a premature vulcanization trigger, reducing scorch safety by up to 45% under humid ageing conditions (40°C, 95% RH, 14 days). Storage stability protocols mandate sealed aluminium‑lined fibre drums kept below 25°C and away from direct release agents containing stearic acid, which plasticizes the crystal lattice and depresses the melting onset to 111°C. The vulcanizate is assessed for nitrosamine generation potential by extracting the cured slab with dichloromethane, concentrating, and analysing via GC‑TEA in accordance with ISO 29941. Detected N‑nitrosamines remain below 0.5 µg/kg of rubber, satisfying the limit specified in EU Regulation 2005/69/EC for articles placed on the European market. In tyre compounds, roadwear indicators using this benzothiazole‑based accelerator maintain a tensile strength above 21 MPa (dumbbell die C, ISO 37:2017) and an elongation at break of 480–520% after 10⁶ fatigue cycles on a Monsanto Fatigue‑to‑Failure Tester at 100% extension. Compounds intended for conveyor belts operating in direct contact with mineral‑oil‑based lubricants must be co‑vulcanised with 0.5 phr sulphur donor DTDM; without it, the dynamic crack growth rate under ISO 132 doubles within 72 h of immersion at 70°C.Disperse Dye Intermediates with Intrinsic Alkali Resistance and High Extinction CoefficientsWhen 2-(p-aminophenyl)-6-methylbenzothiazole is developed as a heterocyclic diazo component, the resulting disperse dyes exhibit molar extinction coefficients in dimethylformamide between 38,000 and 52,000 L mol⁻¹ cm⁻¹ at λmax 515–565 nm, considerably higher than common aminoazobenzene‑based benchmarks. The diazotization protocol uses nitrosylsulfuric acid prepared from sodium nitrite in 96% sulfuric acid at −5°C to suppress diazonium salt decomposition; the diazo liquor is then coupled with N‑ethyl‑N‑(2‑hydroxyethyl)aniline at 0–5°C and pH 1.5–2.0 to produce a bluish‑red dye powder after neutralization, filtration, and wash‑drying at 60°C under vacuum. A single 1.0% o.w.f. dyeing on circular‑loom polyester (PET, 0.8 dtex filament) run on a Mathis Univstar AHE‑1 dyeing machine at 130°C for 60 min with a liquor ratio of 1:15 and dispersant (NNO, 1.0 g/L) at pH 5.0 (acetic acid‑sodium acetate buffer) yields a build‑up exceeding 98% bath exhaustion. The dyed substrate exhibits a wet rub fastness of 4–5 and a dry rub fastness of 5 under ISO 105‑X12, without the need for a reduction‑clearing step because the heterocycle imparts high alkali‑hydrolysis resistance. Solvolysis testing in 2% sodium hydroxide at 85°C for 30 min shows less than 4% shade change (ΔE CMC(2:1) < 0.8), which is critical when PES/elastane blends require alkaline reduction of oligomer deposits from Lycra® without bleaching the chromophore.Sublimation fastness measured by ISO 105‑P01 at 180°C × 30 s reaches grade 4–5, consistent with the molecular mass of 428 g/mol and the pronounced planarity of the benzothiazole‑azo linkage that restricts migration in PET amorphous regions. The dye is milled in a Drais wet‑bead mill (zirconia beads, 0.4–0.6 mm) to a particle size distribution where 95% of fines are below 1.0 µm, as verified by a Malvern Mastersizer 3000; poor milling below 0.8 µm median diameter increases dusting and reduces dispersion stability upon storage beyond six months. Formulators are cautioned that the dye interacts unfavourably with SIPA‑based PET copolyesters containing 2–3 mol% sulfonated isophthalate, where the anionic co‑monomer quenches the deep‑red fluorescence and depresses the apparent colour strength (K/S) by 12–15%. In automotive interior fabrics tested to ISO 105‑B06 method 3 (xenon arc, 50 MJ/m²) the dye retains ≥80% of original strength, meeting OEM specification DBL 0‑2 for seat upholstery.A photoinitiating system operating in the near‑UV/visible boundary exploits the electron‑rich p‑aminophenyl group of 2-(p-aminophenyl)-6-methylbenzothiazole as a co‑sensitizer for cationic epoxy polymerization. The formulation comprises 3.5–4.0 wt% of the benzothiazole derivative, 1.0 wt% of diphenyliodonium hexafluorophosphate (Omnicat 820), and 0.5 wt% of 2‑isopropylthioxanthone (ITX) dissolved in a cycloaliphatic epoxy resin (3,4‑epoxycyclohexylmethyl‑3,4‑epoxycyclohexane carboxylate, EEW 128–140 g/eq). Exposure to a 395 nm UV‑LED array delivering 2.5 W/cm² at the coating surface for 2.0 s triggers an electron‑transfer cascade: the excited benzothiazole donates an electron to the iodonium salt, generating initiating protons with a polymerisation peak exotherm of 185 J/g recorded by photo‑DSC (TA Instruments Q2000). Through‑cure of a 30 µm wet film on polyethylene terephthalate is confirmed by zero tack at the back side after 25 double rubs with methyl ethyl ketone (ASTM D5402‑19). Pendulum hardness (König, DIN 53157) develops from 20 s directly after irradiation to 175 s after 24 h dark storage at 23°C, evidencing post‑cure via latent acid. The combination is incompatible with vinyl ether blends because the amino component prematurely generates an amine‑diphenyliodonium charge‑transfer complex that gels with a pot life of less than 45 min under amber light. When the formulation is pigmented with 2.0% rutile TiO₂ (Kronos 2310), the LED irradiance must be increased to 4.0 W/cm² to compensate for scattering losses; otherwise, surface oxygen inhibition leaves a sticky 300–400 nm-thick under‑cured layer detectable by ATR‑FTIR via residual epoxide peak at 790 cm⁻¹. The cured coating passes ≤10% haze after 1,000 h of QUV‑B exposure (ISO 16474‑3) due to the inherently high photostability of the benzothiazole ring.When Ratiometric Cu²⁺ Fluorescent Probes Require Sub‑Ppb Limit of Detection in Hard WaterAn analytical niche application of 2-(p-aminophenyl)-6-methylbenzothiazole stems from the ability of the donor–acceptor architecture to chelate transition metals with accompanying ratiometric fluorescence changes. A probe stock solution prepared in tetrahydrofuran‑water (4:1 v/v, 10 µM) exhibits a dominant emission at 428 nm (λex 330 nm) assigned to an intramolecular charge‑transfer excited state. Titration with Cu²⁺ perchlorate in 10 mM HEPES buffer at pH 7.4 and total ionic strength 0.1 M (NaCl) progressively quenches the 428 nm band while a new structured emission grows at 375 nm with an isoemissive point at 402 nm, enabling ratiometric detection unaffected by photobleaching or lamp drift. The Stern‑Volmer constant measured under continuous‑wave excitation is 2.8×10⁴ M⁻¹; the low‑end linear dynamic range extends from 0.05 to 8.0 µM Cu²⁺, which corresponds to 3.2–508 µg/L in the receiving solution prior to dilution. Even in the presence of 250 mg/L CaCO₃ hardness (typical of borewell water in Chennai or the US Southwest), the quenching efficiency deviates by less than ±6%, owing to the soft nitrogen‑sulfur donor set that discriminates against group II metals. A comparative spike‑recovery study on certified drinking water reference material (ERM‑CA011a, Community Bureau of Reference) yields 97–103% recovery (n=6) when the probe solution is used with a portable fiber‑optic fluorimeter (Ocean Insight QE Pro) and a 5 cm pathlength cuvette, achieving a calculated detection limit (3σ/slope) of 0.08 µg/L. This places the method within the sensitivity corridor required for monitoring compliance with the US EPA Lead and Copper Rule (40 CFR 141.80, copper action level 1.3 mg/L) while allowing on‑site screening without graphite‑furnace atomic absorption spectrometry. The probe is deactivated by contact with persulfate or hypochlorite because oxidation of the p‑aminophenyl group to a nitro or azo derivative collapses the charge‑transfer transition, an effect exploited for quality control of municipal chlorinated supplies. Stored in the dark at −20°C under argon, the solid 2-(p-aminophenyl)-6-methylbenzothiazole retains >95% of initial fluorescence response after 18 months; solution preparations in THF‑water degrade within 72 h when left in clear borosilicate glass on the bench top at 22°C under ambient fluorescent lighting (UVA intensity 0.8 mW/cm²), forming a non‑emissive dimer as confirmed by HRMS. |
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2-(p-Aminophenyl)-6-methylbenzothiazole (CAS 92-36-4; molecular formula C14H12N2S, molecular weight 240.32 g·mol⁻¹) functions as a heterocyclic arylamine intermediate within the synthesis chain of high-performance azo disperse dyes and fluorescent whitening agents. The crystalline solid, typically isolated as a pale yellow to beige powder with a melting endotherm onset at 191–195 °C, bears a primary aromatic amine group para to the benzothiazole ring junction and a methyl substituent at the 6-position. Industrial consumption centers on its conversion to diazonium salts for coupling onto electron-rich aromatic substrates, where the electron-donating character of the 6-methyl group alters the bathochromic shift and substantivity profile relative to the unsubstituted or halo-substituted analogues. Published toxicological data for this specific aminophenylbenzothiazole remain sparse; handling therefore aligns with GHS precautionary statements for aromatic amines, including local exhaust ventilation and impervious nitrile gloves rated for chemical breakthrough times exceeding 30 minutes per EN 374-3.
Substitution at the benzothiazole 6-position modulates the electron density of the fused heterocyclic system. A methyl group exerts a weak positive inductive effect (+I) and negligible mesomeric contribution, raising the ground-state electron density at the diazotizable amino group without significantly perturbing the π→π* transition dipole of the derived chromophore. This contrasts with a 6-methoxy substituent, which introduces a stronger +M effect and a measurable hypsochromic shift in the azo dye absorption maximum, and a 6-chloro group, which withdraws electrons inductively, bathochromically shifting the λmax by 10–15 nm relative to the methyl analogue. In dye synthesis, a kinetic consequence is observed: the diazotization rate of the amine hydrochloride in aqueous HCl at 0–5 °C proceeds within 45–60 minutes at a 1.02 molar equivalent of NaNO₂. The resulting diazonium salt couples more rapidly with β-naphthol derivatives than its 6-methoxy counterpart, a behaviour exploited in multi-component dyeing where short coupling half-lives reduce colour transfer between fabric lots. The table below compares model azo derivatives synthesised from three 6-substituted 2-(p-aminophenyl)benzothiazoles coupled to N-ethyl-N-cyanoethylaniline under standardised laboratory conditions.
| 6-Substituent | λmax (DMF) / nm | Molar extinction coefficient εmax / L·mol⁻¹·cm⁻¹ | Lightfastness AATCC TM16-2019 (Xenon arc, 40 AFU) | Sublimation fastness ISO 105-P01:1993 (210 °C, 30 s) |
|---|---|---|---|---|
| –CH₃ (methyl) | 524 | 45 500 | 6–7 | 4–5 |
| –H | 516 | 42 000 | 6 | 4 |
| –Cl | 537 | 48 200 | 7 | 4–5 |
The methyl analogue occupies a middle ground in tinctorial strength—its higher εmax compared to the unsubstituted derivative but slightly lower than the chloro variant enables compounding flexibility. In mass-coloured polyester fibre, an addition rate of 0.5 wt% of the 6-methyl dye achieves a colour depth K/S value within 5% of that attained by 0.48 wt% of the 6-chloro analogue, measured on a bench-top spectrophotometer equipped with integrating sphere (D65 illuminant, 10° observer).
Commercial lots are commonly supplied with a certificate of analysis conforming to the following release criteria, established by external calibration against NIST-traceable reference standards. Moisture ingress during ocean freight is a documented cause of batch-to-batch variability exceeding ±0.3% in purity, hence sealed 25 kg fibre drums with EVOH barrier liners are specified for intercontinental shipment.
| Parameter | Method | Limit |
|---|---|---|
| Appearance | Visual (CIE Lab, D65) | Pale yellow to beige powder |
| Purity (HPLC, area%) | In-house RP-HPLC, C18 column, UV 254 nm | ≥ 98.5% |
| Major organic impurity (2-(p-nitrophenyl)-6-methylbenzothiazole) | Same HPLC method | ≤ 0.5% |
| Isomer content (2-(m-aminophenyl)-6-methylbenzothiazole) | HPLC, verified by retention time vs. standard | ≤ 1.0% |
| Melting range | DSC, 10 °C·min⁻¹, nitrogen | 191–195 °C |
| Loss on drying (60 °C, vacuum, 4 h) | Gravimetric | ≤ 0.3% |
| Residue on ignition (650 °C) | Gravimetric | ≤ 0.1% |
| Heavy metals (Pb, Cd, Hg, Cr(VI)) | ICP-OES after acid digestion | Each ≤ 10 mg·kg⁻¹ |
The nitrophenyl impurity originates from incomplete reduction of the precursor 2-(p-nitrophenyl)-6-methylbenzothiazole during catalytic hydrogenation. In subsequent diazotisation, residual nitro compound remains inert but depresses effective amine titer, shifting stoichiometric balance; formulators compensating by overcharging nitrite risk nitrosamine formation. The isomer impurity (meta-amino) arises from positional selectivity limits in the initial ring-closure condensation; its presence at > 1.0% broadens the melting endotherm and yields a second diazo component that alters the shade of the final dye.
Temperature-sensitive diazotization and tar formation thresholds demand exacting thermal control that cannot be relaxed when scaling from laboratory glassware to production vessels. A 1000 L glass-lined reactor with jacket capacity for brine at −12 °C is equipped with a retreat-curve impeller operating at 55–65 rpm. The slurry of amine hydrochloride in aqueous HCl (2.5 molar equivalents, 30% excess over stoichiometric to maintain soluble aminium ion) is pre-cooled to 0 °C. Sodium nitrite solution (40% w/w) is metered below the liquid surface through a dip-pipe at a rate that keeps the internal temperature from exceeding 3 °C; typical addition duration spans 60–75 minutes at this scale. A negative starch-iodide test at the end of addition confirms absence of free nitrous acid. At internal temperatures above 8 °C, decomposition of the diazonium salt becomes autocatalytic, releasing nitrogen gas and generating intractable brown tars that foul reactor walls and downstream heat exchangers. Batch records from a specialty dye manufacturer indicate that a single excursion to 12 °C for 4 minutes was sufficient to reduce isolated azo dye yield by 22% and double the filtration time for clarifying the coupler solution. For this reason, in-process temperature trending by three RTD probes spaced across the reactor radius is treated as a critical control point within the plant’s ISO 9001:2015 quality plan, and the diazo liquor is transferred to the coupling reactor within 90 minutes of endpoint, maintained at 0–2 °C by jacketed transfer lines.
The compound functions not as a direct optical brightener but as a building block for benzothiazole-stilbene derivatives produced by condensation with terephthalaldehyde under alkaline conditions. When the resultant bis-benzothiazolylstilbene is dispersed in linear low-density polyethylene (LLDPE) at a masterbatch loading of 1500 ppm active substance, whiteness measured according to ISO 2470-1:2016 rises by 12–18 CIE WI points relative to the unmodified polymer. The 6-methyl group confers a 4–6 °C increase in the onset of sublimation weight loss as determined by TGA at 10 °C·min⁻¹ under nitrogen, which directly translates into reduced plate-out on die lips during cast-film extrusion at 230–250 °C. A parallel application exists in polyester fibre: during high-temperature exhaust dyeing at 130 °C, a brightener derived from the 6-methyl intermediate resists hydrolysis of the sulfonate solubilising groups better than the 6-methoxy analogue, retaining 90% of initial whiteness after 5 commercial laundry cycles per ISO 105-C06:2010 (programme A2S, 60 °C).
Where fastness to perchloroethylene dry-cleaning solvents is paramount, the 6-methyl derivative’s slight lipophilicity advantage over the unsubstituted analogue reduces dye bleed from polyester fibre. Gravimetric extraction tests conducted at 40 °C for 30 minutes in tetrachloroethylene per ISO 105-D02:2016 show colour loss corresponding to ΔE CMC(2:1) < 1.0 for a 6-methyl based anthraquinone-type structure, compared to ΔE 1.8 for the 6-H compound at equal depth. In thermosol processing of polyester-cotton blends, the disperse dye paste containing the 6-methyl diazo component requires a slightly lower fixation temperature—a reduction of < 3 °C is observable in differential scanning calorimetry of the dye-fibre transition—but the practical benefit is narrowed dwell-time window: pad bath stability monitoring is essential beyond 6 hours because weakly acidic conditions (pH 4.5–5.0) catalyse slow diazo migration into cotton fibres, causing wash-off problems. Operators employing the 6-methyl grade must therefore integrate an inline pH sensor with feedback-controlled dosing of monocodium phosphate buffer to maintain pH within ± 0.2 units across the trough.
Storage instructions stipulate that unopened units be kept at 15–25 °C, protected from direct sunlight and segregated from oxidising agents. When relative humidity in the warehouse exceeds 60%, pre-drying at 40 °C and 5 kPa absolute pressure for 6 hours is required before any water-sensitive condensation reaction. The product has shown incompatibility with strong alkalis and anhydrous Lewis acids, which catalyse ring-opening of the thiazole moiety. Under recommended conditions, retest dating of 24 months from the date of manufacture is applied after empirical stability trials confirmed less than 0.2% purity drift over that interval when packaged under nitrogen headspace with a residual oxygen content below 5000 ppm.
